To reuse a similar calculation in multiple locations in your spreadsheet, you can copy and paste functions and formulas from one cell to other cells.
Select the cell, then tap Copy.
Select the cell where you want to paste the formula, then tap Paste.
Tap Paste Formulas.
Double-tap the cell that contains the formula or function you want to copy.
Tap at the end of the formula or function in the input bar at the top of the keyboard, then tap Select All.
Drag the blue selection handles to encompass only the parts of the formula you want to copy.
Tap Copy.
Double-tap the cell where you want to paste the formula or function.
Tap
to the left of the input bar above the keyboard, then double-tap the input bar.
Tap Paste.
You can copy only the result of a formula cell and paste it to another cell.
Select the cell, then tap Copy.
Select the cell where you want to paste the formula, then tap Paste.
Tap Paste Values.